For many years there have been problems in achieving reliable temporary retention of the distal end of a catheter, by increasing the catheter tip section. A variety of solutions have been proposed and used. Perhaps the most common is to use a balloon. An example of such use can be found in a Foley bladder catheter. A balloon, however, has the disadvantages that it constitutes an undesirably large foreign body in the bladder, and that it requires an inflation channel in the wall of the catheter and an external means of inflating the catheter with a valve mechanism. This complicates the design of the catheter, reduces the maximum available lumen section for a given outside diameter and increases the external bulk of the catheter by the presence of an inflation funnel.
An alternative method of catheter retention uses a resiliently protruding formation which can be elastically deformed by an actuator to a non-protruding disposition for catheter insertion and removal. Examples are (i) "ears" formed from the catheter wall (Malecot catheters) or (ii) an increased diameter portion of the catheter tube at the tip thereof (De Pezzer).
These catheters suffer from a variety of problems. Firstly the "ears" may be so flexible that they do not give sufficient retention and may collapse if a slight pull is applied. The De Pezzer type of catheter tends not to give good retention as the diameter at the swollen tip of the catheter is limited. Additionally, it may be difficult to straighten out the swollen tip completely for insertion or removal.
Yet another method of catheter retention is to hold a tip formation in a protruding disposition by tension in an actuating rod or line which extends to the proximal end of the catheter. See British Patent Specification Nos. 688450, 955490, 1014570, 1046478 and 1463269 and U.S Pat. Nos. 1,828,986, 3,241,554, 3,261,357, 3,713,447 and 4,228,802. The catheters disclosed in these documents share the disadvantage of the balloon catheters, that the end of the catheter external to the patient (herein called the "outer" end) is cluttered by the presence of a tip erection means and that the lumen section available during use of the catheter is reduced by a connection between the tip and its erection means.
U.S Pat. No. 3,490,457 to Petersen discloses a catheter in which wings are brought into a projecting disposition by pulling on a tip insert tube with a thread which extends the length of the catheter tube to its proximal end. When the wings are erect the thread is removed.
Insertion of the catheter is effected by an obturator which is a stainless steel rod running the length of the catheter tube. The rod is of course removed after insertion and prior to use of the catheter.
The Petersen arrangement has a number of disadvantages. The thread arrangement is tricky to use. If the thread slips from the insert tube before the wings are erect the catheter must be discarded because the thread cannot be re-connected to complete the task. The insert tube is a tight sliding friction fit at all times in the catheter tube, so there is from beginning to end of the movement of the insert tube to erect the wings a considerable tension in the thread.
Further, there is possible substantially unimpeded flow of liquid along the catheter tube to the proximal end from the moment the distal end enters the bladder or other bodily fluid cavity. Such flow is inconvenient and could be unhygienic.